Processes for forming an aldehyde by the reaction of an olefin with carbon monoxide and hydrogen in the presence of a rhodium-triarylphosphine complex catalyst in the presence of an excess of free triarylphosphine ligand to produce aldehydes rich in the normal isomer are well known in the art as seen for example by U.S. Pat. No. 3,527,809 and Belgium Patent No. 853,377. It is also known that, under hydroformylation conditions, some of the product aldehydes may condense to form by-product, high boiling aldehyde condensation products such as aldehyde dimers and trimers which may serve as solvents for the hydroformylation process as seen for example by U.S. Pat. No. 4,148,830. It has further been observed that the presence of alkyldiarylphosphine (such as propyldiphenylphosphine or ethyldiphenylphosphine) in the rhodium-catalyzed hydroformylation of propylene inhibits catalyst productivity and that when triarylphosphine ligand is employed in the hydroformylation of an alpha-olefin, alkyldiarylphosphine is produced in situ, the "alkyl" group thereof being derived from the alpha-olefin undergoing hydroformylation and the "aryl" groups thereof being the same as the aryl of the triarylphosphine. While Belgium patent No. 863,267 teaches that the presence of such alkyldiarylphosphine can be compensated for by controlling the hydroformylation conditions of the process, the continued build-up of alkyl substituted phosphine over a period of time in a continuous hydroformylation process to produce aldehydes rich in the normal isomer will eventually lead to an unacceptable decrease in the rate of reaction and activity of the rhodium complex catalyst due to the affinity of said alkyl substituted phosphine for the rhodium catalyst.
More recently U.S. application Ser. Nos. 40,913 and 108,279 filed May 21, 1979 and Dec. 28, 1979 respectively, now U.S. Pat. No. 4,283,304, disclose removing triorganophosphine from a composition containing a rhodium complex hydroformylation catalyst or concentrate of said composition by treating said composition or concentrate with an alpha, beta-unsaturated compound or anhydride thereof, such as maleic acid or maleic anhydride. The process is particularly useful for selectively removing alkyl substituted phosphine from said compositions in order to rejuvenate the activity of the rhodium complex catalyst.
However, even after enhancing the activity of the rhodium complex catalyst by removal of alkyl substituted phosphine from the hydroformylation reaction medium, eventually the rhodium complex catalyst will become spent (that is to say such enhancing procedures cannot be repeated indefinitely since eventually the activity of the catalyst will have decreased to such a point that it is no longer economically desirable to operate the hydroformylation process) and the catalyst will have to be replaced. Moreover, improper procedures and/or contaminates, and the like at the initial start-up of a hydroformylation process could result in the early formation of an undesirable hydroformylation medium that must also be replaced.
Upon such occurrences it becomes important to recover the rhodium values of the complex catalyst due to the inordinately high cost of rhodium. Such recovery methods will obviously entail the removal and/or destruction of the organic compounds of the hydroformylation composition, and such poses the problem of what to do with the large excess of triarylphosphine that must be removed from the catalyst solution. For example U.S. application Ser. Nos. 58,123 abandoned and now U.S. Pat. Nos. 4,097,239 and 120,101 filed July 16, 1979 and Feb. 28, 1980 respectively, (the entire disclosures of which are incorporated herein by reference thereto) disclose methods for concentrating a spent hydroformylation medium containing a rhodium complex catalyst via distillation to produce a rhodium complex concentrate which can serve as the source of reactivated rhodium for a rhodium complex hydroformylation process. Such methods result in an organic liquid distillate containing alkyl substituted phosphine and a large excess of triarylphosphine. Accordingly methods which allow for the selective removal of alkyl substituted phosphine from an organic liquid containing alkyl substituted phosphine and triarylphosphine can be clearly beneficial to the state of the art since they can provide an excellent means for rejuvenating the activity of a spent rhodium complex catalyst or for recovering and obtaining large amounts of previously used triarylphosphine for reuse in a hydroformylation process.